The aim of the planned research is the study of the effects of opiates on single neurons of the mammalian brain. The techniques used will be electrophysiological and histological. The excitable properties and synaptic connections of single neurons in the isolated locus coeruleus of the rat will be measured with intracellular recording. Slices of pons will be maintained in vitro for several hours to days, and drugs and opioid peptides will be applied by adding them to the perfusing solution or by pressure ejection from micropipettes. The mechanism of the acute hyperpolarizing effect of opiates will be investigated by changing the ionic environment of the cells. The effects of exogenous opioid peptides will be compared with the effects of endogenous synaptic transmitters released by nerve stimulation, with particular reference to ionic mechanism and sensitivity to enantiomers of opiate antagonists. The effects of prolonged exposure to opiate agonists both in vitro and in vivo will be examined in an effort to elucidate the changes in neuronal excitability which underlie tolerance and dependence. The proposed study represents a most direct way to investigate the actions of opiates on the signalling function of neurons in a brain region known to be pivotal to opiate action. It avoids many of the pitfalls of in vivo extracellular recording yet is more directly relevant than studies on peripheral tissue or cultured neurons. The results are expected to elucidate the primary actions of opiates on neurons, to differentiate between these actions and the long term effects which form the basis of tolerance and dependence, and to establish any functional role which may exist for endogenous opioid peptides at the single neuron level.